The present invention relates to apparatus for mounting on an aircraft, and particularly a missile, a sensor adapted to search an area in two dimensions for a target located at some unknown point. Most prior art mounts for sensors of this type are two degree of freedom devices which are unable to provide roll compensation as the missile or other aircraft rotates about its roll axis. As a result, and unless the missile is roll-stabilized about its longitudinal axis, image smearing will occur, meaning that the target will appear to move through an arc while, in fact, it is not. This smearing can result in the introduction of steering errors to the missile guidance system or the loss of signal if the signal strength is low and the missile is allowed to rotate at a high rate.
The usual technique for reducing image blurring to acceptable levels is to provide a roll control system for the missile. This, however, is an expensive solution requiring a gyro to detect roll motions, a closed-loop feedback control system to generate corrective commands, and an aerodynamic, reactive or propulsive control force mechanism to implement the corrective commands. Furthermore, a roll control system of this type still permits the missile to roll about its center line or longitudinal axis within tolerance limits. The acceptable angular roll rate is a function of the type of seeker and the information sampling rate at which the seeker is interrogated.